The following provides facts about the moisture-shrinkage relationship of
wood. A table of shrinkage values for North American hardwoods and
softwoods is provided after the text.

Green Wood And Fiber Saturation Point

Moisture in wood can exist as water or water vapor in cell cavities, or
lumens, or as water bound chemically within the cell walls. Green wood
is deigned as wood in which cell walls are completely saturated with
water; however, green wood usually contains additional water in the cell
cavities. The moisture content at which the cell walls are completely
saturated but the cell cavities contain no water is called the "fiber
saturation point." The fiber saturation point of wood averages about 30
percent moisture content, but individual species and individual pieces of
wood may vary by several percentage points from that value.

The fiber saturation point often is considered as that moisture content
below which the physical and mechanical properties of wood begin to
change as a function of moisture content. In other words, once the
moisture content of wood reaches 30 percent no more dimensional changes
will occur as more water is added to the wood.

Shrinkage

Wood is dimensionally stable when the moisture content is above the fiber
saturation point. Wood changes dimension as it gains or loses moisture
below that point. It shrinks when losing moisture from the cell walls
and swells when gaining moisture in the cell walls. This shrinking may
result in warping, checking, splitting, or performance problems that
detract from the woods usefulness.

Wood is an anisotropic (not homogeneous in terms of directionality)
material in shrinkage characteristics. It shrinks most in the direction
of annual growth rings (tangentially), about one-half as much across the
rings (radially), and only slightly along the grain (longitudinally).
The combined effects of radial and tangential shrinkage can distort the
shape of wood pieces because of the difference in shrinkage and the
curvature of the annual rings.

The shrinkage of wood is affected by a number of variables. In general,
greater shrinkage is associated with greater wood density. The size and
shape of the wood may also affect shrinkage, as may the temperature and
rate of drying for some species. Longitudinal shrinkage of wood
(shrinkage parallel to the grain) is quite small. The longitudinal
shrinkage from green to oven-dry condition is only 0.1 to 0.2 percent for
most species of wood...so small, that it can usually be ignored.

Shrinkage Values Of Domestic Hardwoods

Shrinkage from green to oven-dry moisture content

Species

Radial
(%)

Tangential
(%)

Alder, red

4.4

7.3

Ash, black

5.0

7.8

Ash, blue

3.9

6.5

Ash, green

4.6

7.1

Ash, oregon

4.1

8.1

Ash, pumpkin

3.7

6.3

Ash, white

4.9

7.8

Aspen, bigtooth

3.3

7.9

Aspen, quaking

3.5

6.7

Basswood, American

6.6

9.3

Birch, Alaska paper

6.5

9.9

Birch, Gray

5.2

?

Birch, Paper

6.3

8.6

Birch, River

4.7

9.2

Birch, Sweet

6.5

9.0

Birch, Yellow

7.3

9.5

Buckeye, Yellow

3.6

8.1

Butternut

3.4

6.4

Cherry, Black

3.7

7.1

Chestnut, American

3.4

6.7

Balsam poplar

3.0

7.1

Cottonwood, Black

3.6

8.6

Cottonwood, Eastern

3.9

9.2

Elm, American

4.2

7.2

Cedar

4.7

10.2

Rock

4.8

8.1

Slippery

4.9

8.9

Elm, Winged

5.3

11.6

Hackberry

4.8

8.9

Pecan

4.9

8.9

Hickory, Mockernut

7.7

11.0

Pignut

7.2

11.5

Shagbark

7.0

10.5

Hickory, Shellbark

7.6

12.6

Holly, American

4.8

9.9

Locust, Honey

4.2

6.6

Locust, Black

4.6

7.2

Madrone, Pacific

5.6

12.4

Magnolia, Cucumber tree

5.2

8.8

Magnolia, Southern

5.4

6.6

Magnolia, Sweetbay

4.7

8.3

Maple, Bigleaf

3.7

7.1

Maple, Black

4.8

9.3

Maple, Red

4.0

8.2

Maple, Silver

3.0

7.2

Maple, Striped

3.2

8.6

Maple, Sugar

4.8

9.9

Oak, Black

4.4

11.1

Oak, Laurel

4.0

9.9

Oak, Northern Red

4.0

8.6

Oak, Pin

4.3

9.5

Oak, Scarlet

4.4

10.8

Oak, Southern Red

4.7

11.3

Oak, Water

4.4

9.8

Oak, Willow

5.0

9.6

Oak, Bur

4.4

8.8

Oak, Chestnut

5.3

10.8

Oak, Live

6.6

9.5

Oak, Overcup

5.3

12.7

Oak, Post

5.4

9.8

Oak, Swamp Chestnut

5.2

10.8

Oak, White

5.6

10.5

Persimmon, Common

7.9

11.2

Sassafras

4.0

6.2

Sweetgum

5.3

10.2

Sycamore, American

5.0

8.4

Tanoak

4.9

11.7

Tupelo, Black

5.1

8.7

Tupelo, Water

4.2

7.6

Walnut, Black

5.5

7.8

Willow, Black

3.3

8.7

Yellow Poplar, Tulip

4.6

8.2

Shrinkage Values Of Domestic Softwoods

Shrinkage from green to oven-dry moisture content

Species

Radial
(%)

Tangential
(%)

Bald cypress

3.8

6.2

Cedar, Alaska

2.8

6.0

Cedar, Atlantic White

2.9

5.4

Cedar, Eastern Red

3.1

4.7

Cedar, Incense

3.3

5.2

Cedar, Northern White

2.2

4.9

Cedar, Port-Orford

4.6

6.9

Cedar, Western Red

2.4

5.0

Douglas-fir, Coastal

4.8

7.6

Douglas-fir, Interior, north

3.8

6.9

Douglas-fir, Interior, west

4.8

7.5

Fir, Balsam

2.9

6.9

Fir, California Red

4.5

7.9

Fir, Grand

3.4

7.5

Fir, Noble

4.3

8.3

Fir, Pacific Silver

4.4

9.2

Fir, Subalpine

2.6

7.4

Fir, White

3.3

7.0

Hemlock, Eastern

3.0

6.8

Hemlock, Mountain

4.4

7.1

Hemlock, Western

4.2

7.8

Larch, Western

4.5

9.1

Pine, Eastern White

2.1

6.1

Pine, Jack

3.7

6.6

Pine, Loblolly

4.8

7.4

Pine, Lodgepole

4.3

6.7

Pine, Longleaf

5.1

7.5

Pine, Pitch

4.0

7.1

Pine, Pond

5.1

7.1

Pine, Ponderosa

3.9

6.2

Pine, Red

3.8

7.2

Pine, Shortleaf

4.6

7.7

Pine, Slash

5.4

7.6

Pine, Sugar

2.9

5.6

Pine, Virginia

4.2

7.2

Pine, Western White

4.1

7.4

Redwood, Old-growth

2.6

4.4

Redwood, Young-growth

2.2

4.9

Spruce, Black

4.1

6.8

Spruce, Englemann

3.8

7.1

Spruce, Red

3.8

7.8

Spruce, Sitka

4.3

7.5

Tamarack

3.7

7.4

The percentages are expressed as a percentage of shrinkage FROM the
green dimension, NOT the swelling from the oven-dry dimension.

(This is an excellent reference book that costs about $25
from the U.S. Printing Office. Just call their number
and say that you'd like to order the USDA, Ag. Handbook,
No. 72)

Panshin, A.J. and Carl de Zeeuw. 1980.
Textbook of Wood Technology:
Structure, Identification, Properties, and Uses of the
Commercial Woods of the United States and Canada.4th Edition
McGraw-Hill Book Company. New York. 722 pages.